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Biomedical subjects

E A Montalvo

Publications and source records attributed to E A Montalvo.

17 recordsLinked to original sources
PubMed2001

Characterization of the promoter region of the viral interferon regulatory factor encoded by Kaposi's sarcoma-associated herpesvirus.

Viral interferon regulatory factor (vIRF) encoded by Kaposi's sarcoma-associated herpesvirus (KSHV) inhibits the expression of interferon-responsive genes, causes cellular transformation and transactivates KSHV genes. In the present study, we characterized the mRNA expression pattern of the vIRF gene and its promoter. A vIRF transcript of 1.7 kb in size was detected in low level in uninduced KSHV-infected cells and its expression was inducible by 12-O-tetradecanoylphorbol-13-acetate (TPA), sensitive to cycloheximide and resistant to phosphonoacetic acid. The transcription start site was mapped to 79 nt upstream of the ATG initiation site by 5'-RACE. Mutagenesis analysis identified a region between -56 and the transcription start site (+1) as the minimal promoter region that contains a functional TATA box at -27. A region between -337 and -125 contains a repressor domain negated by sequence from -991 to -499 in BCBL-1 cells, a region which was also identified to be responsive to TPA induction. These results demonstrate vIRF as a KSHV early gene, identify its promoter and define the promoter regions that contain regulatory elements controlling vIRF transcription.

Base Sequence↗
PubMed1999

Smubp-2 represses the Epstein-Barr virus lytic switch promoter.

Smubp-2 is a novel transcription factor that was first identified through its interaction with the immunoglobulin Smu region (Mizuta et al., 1993) and has been cloned by virtue of its binding to two 12-O-tetradecanoylphorbol-13-acetate-responsive elements in the Epstein-Barr virus immediate-early BZLF1 promoter (Gulley et al., 1997). In this report, we examined the effect of Smubp-2 overexpression on BZLF1 prom oter activity. Overexpression of Smubp-2 in the B lymphocyte cell line BJAB caused repression of the BZLF1 gene promoter. A 14-bp region that partially overlaps with a 12-O-tetradecanoylphorbol-13-acetate-responsive element was required for maximal repression by Smubp-2, but some repression was also seen with a minimal promoter containing only the BZLF1 promoter TATA box and an initiation site. A 30-bp fragment containing the 14-bp region could transfer Smubp-2-mediated repression to heterologous promoters. Smubp-2 was found to associate with the basal transcription factor TATA binding protein (TBP) and to disrupt the formation of a stable TBP-TFIIA-DNA complex on the BZLF1 promoter TATA box and the adenovirus E1B promoter TATA box. Repression of the BZLF1 promoter by overexpressed Smubp-2 was rescued by overexpression of the basal factor TFIIA. These results suggest that complete repression of the BZLF1 promoter by Smubp-2 involves disruption of a functional TBP-TFIIA-TATA box complex and requires the -93 bp-to--79 bp region of the promoter.

Cell Line↗
PubMed1999

Characterization of natural Epstein-Barr virus infection and replication in smooth muscle cells from a leiomyosarcoma.

Cells from a leiomyosarcoma tumor (LMS-1) from a patient with the acquired immunodeficiency syndrome (AIDS) were explanted, cultured in vitro, and studied by phase-contrast microscopy for morphologic and growth characteristics, immunostaining for cell markers, EBER in situ hybridization and polymerase chain reaction for detection of Epstein-Barr virus (EBV), and immunostaining for expression of EBV antigens. The cells exhibited very slow growth in vitro, with unusual elliptical and spindle-shaped morphology and fragmentation of the cytoplasm into long, tapering, cytoplasmic processes. Greater than 90% of cells expressed diffuse distribution of the smooth muscle isoform of actin by immunoperoxidase staining. Approximately 25% of cells expressed very bright fluorescence by immunostaining of the smooth muscle isoforms of calponin and actin. The majority of cells demonstrated a weak signal for CD21; approximately 5-10% of cells showed a strong signal that was confined to cell surfaces. The cultured cells harbored EBV, and infectious EBV continued to be detected by polymerase chain reaction and virus culture through several passages in vitro. Several EBV antigens were expressed, including latent antigen EBNA-1, immediate-early antigen BZLF1, early antigen EA-D, and late antigens, including viral capsid antigen p160, gp125, and membrane antigen gp350. Human umbilical cord lymphocytes that were transformed with virus isolated from cultured cells yielded immortalized cell lines that expressed EBV antigens similar to other EBV-transformed lymphocyte cell lines. These results confirm that EBV is capable of lytic infection of smooth muscle cells with expression of a repertoire of latent and replicative viral products and production of infectious virus. EBV infection of smooth muscle cells may contribute to the oncogenesis of leiomyosarcomas.

Acquired Immunodeficiency Syndrome↗
PubMed1998

Purification of Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) and analyses of the structural proteins.

The Kaposis's sarcoma-associated herpesvirus (KSHV) infected BCBL-1 cell line, adapted to and grown in medium containing 10% horse serum, was induced to lytic replication with 12-O-tetradecanoylphorbol-13-acetate (TPA) for virus production. Supernatants from induced cells were filtered through a 0.45-microm filter and virions were concentrated by polyethylene glycol extraction and high speed centrifugation. The virus was purified by a glycerol gradient zonal centrifugation step followed by isopycnic separation using positive density negative viscosity gradients. Two visible bands were detected after the final centrifugation step: an upper band that contained a homogenous population of purified virions and a lower band that contained aggregates of purified virus and other cellular debris. Fractionation of purified virion preparations by SDS-PAGE revealed 32 bands with estimated molecular weights between 19 and 280 K in silver stained gels. The glycoprotein bands in purified virus were identified with biotinylated lectins and horseradish peroxidase-labeled streptavidin. Two lectins were used to identify the KSHV glycoproteins: concanavalin A and Ricinus communis agglutinin I. Eight distinct glycoproteins were detected with these lectins. In addition, antisera from KS patients were used to detect immunoreactive proteins in purified virions. An apparent immunodominant band of Mr 94,000 (94 K) was recognized by patients' antisera. Other proteins detected with some of the KS antisera tested corresponded to molecular weights of 57 K, 70 K, 180 K, 200 K and 240 K. The 94 K band was identified as gp94 by Endo F digestion.

Cell Line↗
PubMed1998

Antibodies to Kaposi's sarcoma-associated herpesvirus (human herpesvirus 8) in patients with multiple myeloma.

Kaposi's sarcoma-associated herpesvirus (KSHV) serologic assays were used to detect specific antibodies to KSHV lytic and latent antigens in 27 patients with multiple myeloma, 27 control patients with other cancers, and 50 random blood donors. Antibodies to KSHV recombinant minor capsid antigen orf65 were found in 81% of patients with multiple myeloma, 22% of control patients with other cancers, and 6% of the blood donors. Antibodies to KSHV latent nuclear antigens were found in 52% of patients with multiple myeloma, 26% of control patients with other cancers, and 2% of the blood donors. All of the 11 patients with progressive multiple myeloma were KSHV-seropositive. Antibodies to Epstein-Barr virus nuclear antigen 1 were present in 89% of patients with multiple myeloma, 93% of control patients with other cancers, and 88% of the blood donors. These data support the possible association of KSHV infection with multiple myeloma, particularly with progressive disease.

Antibodies, Viral↗
PubMed1997

Characterization of proteins binding to the ZII element in the Epstein-Barr virus BZLF1 promoter: transactivation by ATF1.

Previous studies have shown that the ZII element in the BZLF1 promoter (P1) is responsive to TPA and anti-immunoglobulin induction. In this report, we have studied the DNA/protein complexes formed when ZII is used as a binding site. Twelve distinct DNA/protein complexes were seen in mobility shift experiments using Akata cell nuclear extracts and radiolabeled ZII. Eleven of these complexes were also formed when either BJAB or Raji cell nuclear extracts were used in the binding reaction. Six DNA/protein complexes were affected by mutations in the core TGACATCA motif of ZII which abolish responsiveness to TPA, anti-immunoglobulin treatment, and HHV6 transactivation. The relative sizes of the proteins in the DNA/protein complexes were determined by UV crosslinking. Four distinct specific binding proteins affected by core mutations in ZII were identified as ATFa, ATF1, ATF2, and c-jun. Overexpression of ATF1 in cotransfection experiments caused transactivation of the wild-type P1 promoter but had no effect on a promoter containing a mutant ZII element. An ATF1 mutant with a deleted DNA binding domain failed to transactivate P1. Overexpression of c-jun, ATFa, or ATF2 had no effect on the wild-type or mutant P1 promoter. Our results suggest that ATF1 interacts with the ZII element and may be involved in Epstein-Barr virus reactivation.

Activating Transcription Factor 1↗
PubMed1995

YY1 binds to and regulates cis-acting negative elements in the Epstein-Barr virus BZLF1 promoter.

A 48-bp cis-acting negative element in the Epstein-Barr virus BZLF1 gene P1 promoter has been described previously. By DNase I footprinting experiments, two regions were identified as the protein-binding sites (previously designated site I and site II). In this report, the cellular transcription factor YY1 has been identified as a protein which binds to both of these elements, now designated ZIVA and ZIVB. Both ZIVA and ZIVB conferred cis-acting negative regulation on an enhancerless simian virus 40 promoter. In cotransfection experiments, overexpression of YY1 caused further repression of the enhancerless simian virus 40 promoter containing either the ZIVA or ZIVB element. Cotransfection of a plasmid expressing antisense to YY1 increased the expression of the heterologous promoter containing ZIVA but not ZIVB. In similar experiments carried out with the P1 promoter, overexpression of YY1 caused downregulation of P1 whereas antisense RNA to YY1 caused a slight increase in expression. Analyses of various P1 mutant constructions revealed additional YY1 sites downstream of ZIVB. Overexpression of YY1 also caused downregulation of a P1 mutant with no apparent YY1-binding sites. TPA treatment of Raji cells caused a temporal loss of YY1-binding activity but had no effect on the intracellular levels of YY1 protein. Serum induction of quiescent B cells also caused loss of YY1 binding to the ZIVB site, which was found to be a weak serum response element. In contrast, anti-immunoglobulin G treatment of Akata cells had no effect on either the YY1-binding activity or protein levels. The binding of YY1 to the cis-acting negative elements in infected B cells may play a pivotal role in the maintenance of Epstein-Barr virus latency.

Base Sequence↗
PubMed1991

Negative regulation of the BZLF1 promoter of Epstein-Barr virus.

The Epstein-Barr virus BZLF1 gene product (ZEBRA) is a transcriptional activator whose expression in latently infected B cells is sufficient to induce the viral lytic cycle. Since there is no transcription of BZLF1 during latency, we carried out experiments to determine whether cis-acting negative elements in the BZLF1 promoter contribute to the lack of expression during this phase of the virus cycle. A series of deletion plasmids encompassing positions -551 to +14 of the BZLF1 promoter region were constructed and tested for the ability to drive chloramphenicol acetyltransferase (CAT) gene expression in the absence of inducing agents such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and anti-immunoglobulin. Expression from the intact 551-bp region was very weak in most of the cell lines tested, but deletion of 165 bp from the 5' end caused a sevenfold increase in expression of CAT. Within these 165 bp, a minimal 48-bp region was sufficient to down regulate the expression of a simian virus 40/CAT fusion plasmid. The 48-bp negative element consists of 7-bp dyad symmetry elements separated by 27 bp. The rightmost half of the dyad symmetry element partially overlaps a region which has a 14-of-15-bp homology to the human cytoskeletal gamma-actin promoter.

Animals↗
PubMed1987

Assembly and processing of the disulfide-linked varicella-zoster virus glycoprotein gpII(140).

Varicella-zoster virus (VZV) specifies the synthesis of at least four families of glycoproteins, which have been designated gpI, gpII, gpIII, and gpIV. In this report we describe the assembly and processing of VZV gpII, a structural protein of an apparent Mr of 140,000, which is the homolog of gB of herpes simplex virus. For these studies, we used two anti-gpII monoclonal antibodies which exhibited both complement-independent neutralization activity and inhibition of virus-induced cell-to-cell fusion. Pulse-chase labeling experiments identified a 124,000-Mr intermediate which was chased to the mature 140,000-Mr product when analyzed in nonreducing gels; in the presence of a reducing agent, the native gp140 was cleaved into two closely migrating species (gp66 and gp68). The biosynthesis of VZV gpII was further analyzed in the presence of the following inhibitors of glycoprotein processing: tunicamycin, monensin, castanospermine, swainsonine, and deoxymannojirimycin. All intermediate and mature forms were digested with endoglycosidases H and F, neuraminidase, and O-glycanase to further define high-mannose, complex, and O-linked glycans. Finally, the addition of sulfate residues was investigated. This characterization of VZV gpII revealed the following results. (i) gp128 and gp124 were early high-mannose forms, (ii) gp126 was an intermediate form with complex N-linked oligosaccharides, (iii) gp130 was a later intermediate with both N-linked and O-linked glycans, and (iv) the mature product gp140 contained a mixture of N-linked and O-linked glycans which were both sialated and sulfated. Further investigations indicated that gpII sulfation was inhibited by tunicamycin and castanospermine but not by deoxymannojirimycin or swainsonine. We also concluded that VZV gpII displayed many biological and biochemical properties similar to those of its herpes simplex virus homolog gB.

1-Deoxynojirimycin↗
PubMed1986

Neutralization epitope of varicella zoster virus on native viral glycoprotein gp118 (VZV glycoprotein gpIII).

Varicella-zoster virus (VZV) specifies the formation of several glycoproteins, including a 118,000-Da mature structural product (gp118). The biologic and biochemical properties of gp118 were studied after production of murine monoclonal antibodies to both a lowpassage laboratory strain (VZV-32) and an attenuated vaccine strain (VZV-Oka). Structural analyses performed with the three glycosidases endo-beta-N-acetylglucosaminidase H (endoglycosidase H), endo-beta-N-acetylglucosaminidase F (endoglycosidase F), and endo-alpha-N-acetylgalactosaminidase demonstrated that gp118 was predominantly an N-linked complex type glycoprotein built upon a polypeptide backbone of approximately 79,000 Da. Sialic acid residues were present on the mature glycoprotein, but these terminal sugars were absent from the partially glycosylated intermediate forms recovered from monensin-treated infected cultures. Unlike another VZV-specified glycoprotein gp98, no new oligosaccharide moieties were observed on gp118 after addition of tunicamycin to VZV-infected cultures. By plaque reduction assays with a panel of monoclonal antibodies, we defined an epitope on this glycoprotein which elicited a complement-independent neutralizing antibody response of high magnitude. The epitope was highly conserved, since it was present on a laboratory VZV strain, wild type isolates, as well as the attenuated vaccine strain (VZV-Oka). Competitive blocking experiments with the same anti-gp118 monoclonal antibodies indicated that four neutralizing antibodies were directed against similar or identical epitopes whereas one nonneutralizing antibody reacted with a different antigenic site. Thus, this study demonstrates the presence of an immunodominant neutralization epitope on native viral glycoprotein gp118. Under a new consensus nomenclature, this glycoprotein will be designated VZV gpIII.

Antibodies, Monoclonal↗
PubMed1986

Varicella zoster virus glycoprotein gpI is selectively phosphorylated by a virus-induced protein kinase.

Varicella zoster virus glycoprotein I (VZV gpI; Mr 98,000) was phosphorylated in virus-infected human cell monolayers, while two other major VZV glycoproteins (gpII and gpIII) were not similarly modified. Phosphorylation of VZV gpI was not blocked by inhibitors of glycosylation, nor were the phosphoryl groups enzymatically removed by endoglycosidases. Phosphoamino acid analysis revealed the presence of phosphoserine and phosphothreonine residues on the polypeptide backbone. The selective nature of the phosphorylation event was further demonstrated in vitro by a protein kinase (Mr 50,000), which was present in virus-infected cells but absent from uninfected cells or purified virions. The enzyme catalyzed the transfer of 32Pi from [gamma-32P]ATP to gpI but not to gpII and gpIII. Like VZV gpI, this virus-induced protein kinase was also a constituent of the plasma membrane of live VZV-infected cells.

Cell Membrane↗
PubMed1986

Varicella-zoster viral glycoprotein envelopment: ultrastructural cytochemical localization.

The periodate-thiocarbohydrazide silver proteinate (PA-TCH-SP) method was used to study the envelopment process in varicella-zoster virus-infected human melanoma cells. Viral envelopment could be seen at two sites, the nuclear membrane and at virus-induced intracytoplasmic vacuoles. Virus-associated glycoconjugates were detected by the PA-TCH-SP method at the plasmalemma and on the inner membrane of the intracytoplasmic vacuoles. Virion envelopes acquired at the nuclear membrane were PA-TCH-SP negative, whereas those acquired at intracytoplasmic vacuoles were PA-TCH-SP positive. All virions found inside these vacuoles contained periodate-reactive envelopes. Release of virions into the extracellular space, where virtually all virions were PA-TCH-SP positive, appeared to be via exocytosis. Thus, the PA-TCH-SP method identifies glycoprotein incorporation at specific cytoplasmic vacuoles distinct from nuclear envelope, endoplasmic reticulum, and Golgi lamellae. These results suggest that envelopment within the cytoplasm is a stage in the assembly of the varicella-zoster virion.

Glycoproteins↗
PubMed1985

Structural analysis of the varicella-zoster virus gp98-gp62 complex: posttranslational addition of N-linked and O-linked oligosaccharide moieties.

Varicella-zoster virus specifies the formation of several glycoproteins, including the preponderant gp98-gp62 glycoprotein complex in the outer membranes of virus-infected cells. These viral glycoproteins are recognized and precipitated by a previously described monoclonal antibody designated monoclone 3B3. When an immunoblot analysis was performed, only gp98 was reactive with monoclone 3B3 antibody; likewise, titration in the presence of increased concentrations of sodium dodecyl sulfate during antigen-antibody incubations caused selective precipitation of gp98 but not gp62. Further structural analyses of gp98 were performed by using the glycosidases endo-beta-N-acetylglucosaminidase H (endoglycosidase H) and neuraminidase and two inhibitors of glycosylation (tunicamycin and monensin). In addition to gp98, antibody 3B3 reacted with several intermediate products, including gp90, gp88, gp81, and a nonglycosylated polypeptide, p73. Since gp98 was completely resistant to digestion with endoglycosidase H, it contained only complex carbohydrate moieties; conversely, gp81 contained mainly high-mannose residues. Polypeptide p73 was immunodetected in the presence of tunicamycin and designated as a nascent recipient of N-linked sugars, whereas gp88 was considered to contain O-linked oligosaccharides because its synthesis was not affected by tunicamycin. The ionophore monensin inhibited production of mature gp98, but other intermediate forms, including gp90, were detected. Since the latter product was similar in molecular weight to the desialated form of gp98, one effect of monensin treatment of varicella-zoster virus-infected cells was to block the addition of N-acetylneuraminic acid. Monensin also blocked insertion of gp98 into the plasma membrane and, as determined by electron microscopy, inhibited envelopment of the nucleocapsid and its transport within the cytoplasm. On the basis of this study, we reached the following conclusions: the primary antibody 3B3-binding epitope is located on gp98, gp98 is a mature product of viral glycoprotein processing, gp98 contains both N-linked and O-linked oligosaccharide side chains, gp90 is the desialated penultimate form of gp98, gp88 is an O-linked intermediate of gp98, gp81 is the high-mannose intermediate of gp98, and p73 is the unglycosylated precursor of gp98.

Cells, Cultured↗
PubMedDate not supplied

Translocations of 11q13 in mantle cell lymphoma fail to disrupt the S mu bp-2 gene.

We recently cloned a gene whose protein product binds to the Epstein-Barr virus BZLF1 gene promoter. The same gene has been previously cloned by another group who named it S mu bp-2 because its protein product binds to the S mu motif of the immunoglobulin heavy chain gene where it is postulated to function in immunoglobulin class switching. In the current study, we confirm that the S mu bp-2 gene is located on chromosome 11q13, a locus known to be altered by translocation in 50-70% of mantle cell lymphomas. We used Southern blot analysis to determine whether the S mu bp-2 gene was structurally rearranged in any of 25 mantle cell lymphomas. We found no evidence of rearrangement in any of these lymphomas including 18 that were proven to contain t(11;14) by cytogenetic analysis. These data suggest that structural alteration of the S mu bp-2 gene is not an underlying mechanism of tumorigenesis in mantle cell lymphomas.

Chromosome Mapping↗